Backlash is the clearance between adjacent gear teeth. More specifically, backlash is the clearance around a tooth of a driver gear as it fills the space between two teeth of a driven gear. Backlash is defined as the rotational arc clearance between a pair of mounted gears. Some amount of backlash (clearance) is necessary in order to permit relative motion between the two gears and to prevent damage from interference. Lack of backlash may cause noise, overloading, overheating of gears, and even seizing and failure. Gears without backlash will not work if temperature rises. In a gear system with no backlash, the meshing of the teeth between the gears will be so tight that, absent any deflection of the teeth, the gears will bind and cause the system to jam.
In a gear system with any degree of backlash, an audible noise known as “lash” is produced by the contact of the teeth of one gear with the teeth of another gear. While lash is not indicative of a defect in the gearing system, it often proves to be an annoyance and it is therefore desired to be minimized as much as practicable. Backlash is a reality in any gear transmission. In every steering system, eliminating backlash is very important, especially in active front control steering systems. Backlash is the sum of the free play between every set of meshing components. Steering systems with backlash have bad feeling at directional changes. At the same time, backlash is lost motion. Furthermore, wear increases backlash over time.